Project Summary There is a fundamental gap in understanding how the physicochemical properties of carbon nanotubes (CNTs) contribute to hazard generation in the lung. Without this knowledge, it is difficult to evaluate CNT safety in a predictive and affordable manner. The long-term goal of our multidisciplinary approach is to develop a predictive toxicological approach for CNT safety assessment in which the physicochemical properties leading to hazardous interactions at the nano/bio interface can be used to understand the materials' pro-inflammatory and pro-fibrogenic effects in the lung. The overall objective of this application is to develop a series of single- wall (SW) and multi-wall carbon nanotube (MWCNT) libraries that can be screened by robust cellular assays to establish quantitative structure activity relationships (SARs) and hazard ranking of the tubes' potential to induce pulmonary damage. Our central hypothesis is that tube dimensions (including length, diameter and aspect ratio), state of dispersion, catalytic surface chemistry, electronic properties and purity play key roles in initiating cooperative cellular interactions in macrophages and cellular elements from the epithelial- mesenchymal trophic unit, which are key to the development of development of pulmonary inflammation and fibrosis. The rationale for the proposed research is that once the quantitative contributions of specific physicochemical properties to hazard generation is known, it will be possible to use a predictive toxicology approach for expedited safety assessment of CNTs as well as their safer design. Guided by strong preliminary data, this hypothesis will be tested by pursuing three specific aims: Aim 1: To develop hazard ranking that relates the properties of well-prepared and characterized MWCNT and SWCNT libraries to mechanistic toxicological responses in epithelial cells and macrophages, with a view to develop quantitative structure- activity relationships (SARs) that predict in vivo injury potential. Aim 2: To develop and validate a predictive toxicological paradigm for pulmonary hazard potential of well-characterized commercial and purified CNTs, using in vitro SAR-based hazard ranking and grouping of materials that can also be used towards a tiered risk assessment approach. Aim 3: To use covalent and non-covalent surface modification to demonstrate the feasibility of safe-by-design approaches for CNTs, using a predictive toxicological approach. Our approach is innovative, because it represents a substantive departure from the status quo, namely the use of purified and well- prepared CNTs that are investigated according to robust toxicological mechanisms that predict the in vivo toxicological outcome. The proposed research is significant because: (i) it addresses the concern of how to perform CNT safety assessment using a robust, quantitative scientific platform; (ii) the establishment of a robust safety platform based on grouping of CNT properties that can be used for control banding and read- across risk assessment; (iii) the research will develop an affordable and rational scientific platform for regulatory decision-making and product approval towards the marketplace.